Steam reforming is one means for feeding hydrogen to a fuel cell. In steam reforming, hydrogen is obtained by the following steps: (i) reacting hydrocarbon and steam with each other to generate carbon monoxide and hydrogen; (ii) further reacting the carbon monoxide and steam with each other to generate carbon dioxide and hydrogen; and (iii) separating the carbon dioxide from a mixed gas that contains the carbon dioxide and the hydrogen.
As a method of separating carbon dioxide from a mixed gas, a membrane separation method has attracted attention in recent years because this method can save energy. As a gas separation membrane used in the membrane separation method, various separation membranes have been proposed. Among such various separation membranes, a facilitated transport separation membrane for separating carbon dioxide is a separation membrane which utilizes a reversible reaction of carbon dioxide and a carbon dioxide carrier, and this facilitated transport separation membrane for separating carbon dioxide has been a subject of vigorous research and development (Patent Literatures 1 and 2). For example, Patent Literature 3 proposes a technique of improving carbon dioxide permeation performance of a carbon dioxide separation membrane. In this technique, water is prevented from evaporating from a permeate side of the carbon dioxide separation membrane by (i) applying a pressure equal to or larger than a saturated steam pressure to the permeate side of the carbon dioxide separation membrane that utilizes a facilitated transport mechanism and (ii) feeding a humidified sweep gas to the permeate side.